Following approval by the FDA (IND #14,115) and our Committee on Clinical Investigations, we instituted and have now completed a preliminary feasibility study of a synthetic polypeptide (Copolymer I) as a potential therapeutic agent for patients with multiple sclerosis (MS). Fifteen patients, affected by either the exacerbating-remitting (ER) or the chronic-progressive (C-P) form of MS, have all been given varying intramuscular doses (from 5 to 20 mgm in 1 ml steril saline) at a rate varying from once a week to once a day. All patients knew they were getting COP I. No significant local or systemic undesirable reactions have been noted. Two E-R and two C-P patients have experienced significant improvements. The other have not been favorably affected, experiencing either exacerbations or chronic progression. It is proposed now to pursue the second phase of the feasibility studies in a select group of 40 or more E-R patients who will be randomly divided into two relatively uniform and matched groups. They will be treated with either 20 mg COP I in 1 ml sterile saline i.m. daily or a placebo of 1 ml sterile saline l.m daily. They will be blinded and evaluated by blinded neurologist-investigators for changes in the incidence and severity of exacerbations. Over a two year period, the neurological evaluations will be performed routinely, pre-treatment and on the 14th day, 28th day, 3, 6, 9, 12, 15, 18, 21 and 24 months after institution of treatment, and weekly at the time(s) of exacerbations. Routine clinical and various experimental studies will be performed on blood, urine, and CSF samples pre-treatment and at various times during and after treatment. Data will be evaluated to determine primarily whether COP I produces a significant (25%) decrease in the incidence of exacerbations in the treated as compared to the placebo group.